In a data processing environment, data is stored on a variety of data storage devices. For example, presently, data is stored on a set of magnetic hard disks, magnetic tape drives, optical data storage devices, solid-state memories, and many other types of data storage devices.
In certain data processing environments, several data processing systems may access a data storage unit. For example, several host computers, or nodes, may access a storage area network (SAN), the SAN including a combination of data storage devices. In certain other data processing environments, different applications in a data processing system may access different portions of a data storage associated with the data processing system.
Typically, an application executing on a data processing system accesses a logical view of certain data storage that is available to the application, the data processing system, or both. For example, a one Terabyte (TB) data storage unit, such as a SAN, may be a combination of several hard disks of two Gigabytes (GB) capacity each. A node or an application executing thereon may not have access to the entire 1 TB SAN, but to a portion, for example, 10 GB, thereof. From the point of view of the node and the application executing thereon, the data storage available to it is of size 10 GB, and not 1 TB.
Such a view of data storage, as in this example, is called a volume, a logical volume, or a logical unit, and has an identifier called Logical Unit Number (LUN) associated therewith. As one example, a LUN may represent all or a portion of a data storage device. In another example, a LUN may represent a combination of two or more portions of one or more data storage devices.
A volume manager is an application that manages read/write access to one or more LUNs. A volume manager is also known as a logical volume manager (LVM). An LVM can manage read/write access to more than one LUNs for one data processing system, or for more than one node, such as in a cluster of nodes in a high availability configuration.